This study evaluated the effects of culture conditions, including carbon and nitrogen sources, L-monosodium glutamate (MSG), and initial pH, on gamma-aminobutyric acid (GABA) production by HYE1 isolated from kimchi, a Korean traditional fermented food. HYE1 was screened by the production analysis of GABA and genetic analysis of the glutamate decarboxylase gene, resulting in 14.64 mM GABA after 48 h of cultivation in MRS medium containing 1% (w/v) MSG. In order to increase GABA production by HYE1, the effects of carbon and nitrogen sources on GABA production were preliminarily investigated via one-factor-at-a-time optimization strategy. As the results, 2% maltose and 3% tryptone were determined to produce 17.93 mM GABA in modified MRS medium with 1% (w/v) MSG. In addition, the optimal MSG concentration and initial pH were determined to be 1% and 5.0, respectively, resulting in production of 18.97 mM GABA. Thereafter, response surface methodology (RSM) was applied to determine the optimal conditions of the above four factors. The results indicate that pH was the most significant factor for GABA production. The optimal culture conditions for maximum GABA production were also determined to be 2.14% (w/v) maltose, 4.01% (w/v) tryptone, 2.38% (w/v) MSG, and an initial pH of 4.74. In these conditions, GABA production by HYE1 was predicted to be 21.44 mM using the RSM model. The experiment was performed under these optimized conditions, resulting in GABA production of 18.76 mM. These results show that the predicted and experimental values of GABA production are in good agreement.

A putative gene (gadlbhye1) encoding glutamate decarboxylase (GAD) was cloned from Lactobacillus brevis HYE1 isolated from kimchi, a traditional Korean fermented vegetable. The amino acid sequences of GADLbHYE1 showed 48% homology with the GadA family and 99% identity with the GadB family from L. brevis. The cloned GADLbHYE1 was functionally expressed in Escherichia coli using inducible expression vectors. The expressed recombinant GADLbHYE1 was successfully purified by Ni-NTA affinity chromatography, and had a molecular mass of 54 kDa with optimal hydrolysis activity at 55 °C and pH 4.0. Its thermal stability was determined to be higher than that of other GADs from L. brevis, based on its melting temperature (75.18 °C). Kinetic parameters including K and V values for GADLbHYE1 were 4.99 mmol/L and 0.224 mmol/L/min, respectively. In addition, the production of gamma-aminobutyric acid in E. coli BL21 harboring gadlbhye1/pET28a was increased by adding pyridoxine as a cheaper coenzyme.

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A Gram-positive, endospore-forming, strictly aerobic and rod-shaped bacterium, designated strain MME2_R6, was isolated from Arctic soil, and it was identified by using a polyphasic taxonomic approach. This strain was psychrotolerant, growing at 4‒24 °C. 16S rRNA gene sequence analysis showed that strain MME2_R6 was closest to Paenibacillus swuensis DY6, with 93.9 % similarity. However, in phylogenetic analysis based on the 16S rRNA gene sequence, strain MME2_R6 showed that it clustered with Paenibacillus contaminans CKOBP-6 and the sequencing similarity between the two species was 93.7 %. Its major cellular fatty acid was anteiso-C15 : 0, like other Paenibacillus species. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. The predominant isoprenoid quinone was menaquinone-7. The diagnostic diamino acid in the cell wall was meso-diaminopimelic acid. The genomic DNA G+C content was 44.2 mol%. Based on the results of phenotypic, chemotaxonomic and phylogenetic analyses, a novel species, Paenibacillus arcticus sp. nov., is proposed. The type strain is MME2_R6 (=JCM 30981=PAMC 28731).

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